Capacitors having a capacitor dielectric layer comprising a metal oxide having multiple different metals bonded with oxygen

ABSTRACT

The invention comprises capacitors having a capacitor dielectric layer comprising a metal oxide having multiple different metals bonded with oxygen. In one embodiment, a capacitor includes first and second conductive electrodes having a high k capacitor dielectric region positioned therebetween. The high k capacitor dielectric region includes a layer of metal oxide having multiple different metals bonded with oxygen. The layer has varying stoichiometry across its thickness. The layer includes an inner region, a middle region, and an outer region. The middle region has a different stoichiometry than both the inner and outer regions.

TECHNICAL FIELD

This invention relates to capacitors having a capacitor dielectric layercomprising a metal oxide having multiple different metals bonded withoxygen.

BACKGROUND OF THE INVENTION

As DRAMs increase in memory cell density, there is a continuingchallenge to maintain sufficiently high storage capacitance despitedecreasing cell area. Additionally, there is a continuing goal tofurther decrease cell area. One principal way of increasing cellcapacitance is through cell structure techniques. Such techniquesinclude three-dimensional cell capacitors, such as trenched or stackedcapacitors. Yet as feature size continues to become smaller and smaller,development of improved materials for cell dielectrics as well as thecell structure are important. The feature size of 256 Mb DRAMs andbeyond will be on the order of 0.25 micron or less, and conventionaldielectrics such as SiO₂ and Si₃N₄ might not be suitable because ofsmall dielectric constants.

Highly integrated memory devices, such as 256 Mbit DRAMs, are expectedto require a very thin dielectric film for the 3-dimensional capacitorof cylindrically stacked or trench structures. To meet this requirement,the capacitor dielectric film thickness will be below 2.5 nm of SiO₂equivalent thickness.

Insulating inorganic metal oxide materials (such as ferroelectricmaterials, perovskite materials and pentoxides) are commonly referred toas “high k” materials due to their high dielectric constants, which makethem attractive as dielectric materials in capacitors, for example forhigh density DRAMs and non-volatile memories. In the context of thisdocument, “high k” means a material having a dielectric constant of atleast 11. Such materials include tantalum pentoxide, barium strontiumtitanate, strontium titanate, barium titanate, lead zirconium titanateand strontium bismuth titanate. Using such materials enables thecreation of much smaller and simpler capacitor structures for a givenstored charge requirement, enabling the packing density dictated byfuture circuit design.

Certain high k dielectric materials have better current leakagecharacteristics in capacitors than other high k dielectric materials. Insome materials, aspects of a high k material which might be modified ortailored to achieve a highest capacitor dielectric constant possiblewill unfortunately also tend to hurt the leakage characteristics (i.e.,increase current leakage). For example, one class of high k capacitordielectric materials includes metal oxides having multiple differentmetals bonded with oxygen, such as the barium strontium titanate, leadzirconium titanate, and strontium bismuth titanate referred to above.For example with respect to barium strontium titanate, it is found thatincreasing titanium concentration as compared to barium and/or strontiumresults in improved leakage characteristics, but decreases thedielectric constant. Accordingly, capacitance can be increased byincreasing the concentration of barium and/or strontium, butunfortunately at the expense of increasing leakage. Further, absence oftitanium in the oxide lattice creates a metal vacancy in such multimetaltitanates which can increase the dielectric constant, but unfortunatelyalso increases the current leakage.

One method of decreasing leakage while maximizing capacitance is toincrease the thickness of the dielectric region in the capacitor.Unfortunately, this is not always desirable. Another prior art method ofdecreasing leakage is described with respect to FIG. 1. Thereillustrated is a semiconductor wafer fragment 10 comprising a bulkmonocrystalline silicon substrate 12. In the context of this document,the term “semiconductor substrate” or “semiconductive substrate” isdefined to mean any construction comprising semiconductive material,including, but not limited to, bulk semiconductive materials such as asemiconductive wafer (either alone or in assemblies comprising othermaterials thereon), and semiconductive material layers (either alone orin assemblies comprising other materials). The term “substrate” refersto any supporting structure, including, but not limited to, thesemiconductive substrates described above. A conductive diffusion region14 is formed within substrate 12. An insulating dielectric layer 16 isformed over substrate 12, and includes an opening 18 formed therein todiffusion region 14. Opening 18 is filled with a suitable conductivematerial 20, for example conductively doped polysilicon or a metal suchas tungsten. Barrier, silicide or other layers might also of course beutilized, but are not otherwise described.

A capacitor construction 22 is formed outwardly of insulating dielectriclayer 16 and in electrical connection with conductive plugging material20. Such comprises an inner capacitor electrode 24, an outer capacitorelectrode 26, and a capacitor dielectric region 25 sandwichedtherebetween. Capacitor dielectric region 25 comprises a composite ofthree layers 26, 27 and 28. Region 27 comprises a layer of metal oxidehaving multiple different metals bonded with oxygen, such as bariumstrontium titanate, fabricated to provide a stoichiometry whichmaximizes the dielectric constant of the material. As referred to above,this unfortunately adversely affects the desired leakage properties ofthe layer. Accordingly, layers 26 and 28 are received outwardly of layer27 and comprise a material such as Si₃N₄ which exhibits extremely lowcurrent leakage. Unfortunately, Si₃N₄ has a considerably lowerdielectric constant than the metal oxides having multiple differentmetals bonded with oxygen. Such adversely reduces the overall dielectricconstant, and accordingly the capacitive effect of capacitor dielectricregion 25.

SUMMARY

The invention comprises capacitors having a capacitor dielectric layercomprising a metal oxide having multiple different metals bonded withoxygen. In one embodiment, a capacitor includes first and secondconductive electrodes having a high k capacitor dielectric regionpositioned therebetween. The high k capacitor dielectric region includesa layer of metal oxide having multiple different metals bonded withoxygen. The layer has varying stoichiometry across its thickness. Thelayer includes an inner region, a middle region, and an outer region.The middle region has a different stoichiometry than both the inner andouter regions.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic view of a semiconductor wafer fragmentprocessed in accordance with the prior art, as discussed in the“Background” section above.

FIG. 2 is a diagrammatic sectional view of a semiconductor waferfragment in accordance with the invention.

FIG. 3 is a diagrammatic view of a chemical vapor deposition chamberutilized in accordance with an aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

The invention is described in one exemplary structural embodiment asdepicted by FIG. 2. Like numerals from the FIG. 1 prior art embodimentare utilized where appropriate, with differences being indicated withdifferent numerals. FIG. 2 depicts a wafer fragment 30 comprising acapacitor 32 having first and second electrodes 24 and 26. Example andpreferred materials for electrodes 24 and 26 include conductively dopedpolysilicon, conductively doped hemispherical grain polysilicon,platinum, ruthenium, ruthenium oxides, iridium, iridium oxides,palladium, tungsten, tungsten nitride, tantalum nitride, titaniumnitride, titanium oxygen nitride, and the like.

A high k capacitor dielectric region 35 is positioned between firstcapacitor electrode 24 and second capacitor electrode 26. Capacitordielectric region 34 comprises a layer of metal oxide having multipledifferent metals bonded with oxygen, for example those materialsdescribed above. Most preferably and as shown, capacitor dielectricregion 35 consists essentially of such layer, meaning no other layersare received intermediate first electrode 24 and second electrode 26which meaningfully impact the operation or capacitance of capacitor 32.In accordance with but one aspect of the invention, the metal oxidelayer having multiple different metals bonded with oxygen has varyingstoichiometry across its thickness. In other words, the stoichiometry insuch layer is not substantially constant throughout the layer.

In accordance with but one aspect of the invention, consider a high kcapacitor dielectric region comprising a layer of metal oxide havingmultiple different metals bonded with oxygen. One of the metals whenbonded with oxygen has a first current leakage potential, while anotherof the metals when bonded with oxygen has a second current leakagepotential which is greater than the first current leakage potential. Byway of example only, consider a titanate, such as barium strontiumtitanate. Titanium is an example of one metal which when bonded withoxygen has a lower current leakage potential than either barium orstrontium when bonded with oxygen. In this embodiment, the layercomprises at least one portion having a greater concentration of the onemetal bonded with oxygen which is more proximate at least one of thefirst and second electrodes than another portion which is more proximatea center of the layer.

By way of example only, capacitor 32 depicts capacitor dielectric regionand layer 35 as comprising an inner region 36, a middle region 38, andan outer region 40. Regions 36 and 40 most preferably constituteportions which are fabricated to have a greater concentration of the onemetal, in this example titanium, bonded with oxygen than portion 38.Accordingly, regions 40 and 36 are more proximate at least one of thefirst and second electrodes than is portion 38 more proximate a centerof the layer within capacitor dielectric region 35.

Accordingly, the layer or region 35 in this example comprises portions36 and 40 having a greater concentration of the one metal bonded withoxygen more proximate both the first and second electrodes than theanother portion 38 more proximate the center of the layer of capacitordielectric region 35. Further preferably, region 38 has a greaterconcentration of the another of the metals (i.e., a greaterconcentration of one or both of barium and strontium) bonded with oxygenthan portions 36 and 40. Further in this preferred example, at least oneof portions 36 and 40 (both of such portions as shown) contacts one ofthe first and second electrodes. As shown, portion 36 contacts electrode24, while portion 40 contacts electrode 26. Regions 36, 38 and 40 can befabricated to be the same thickness or different relative thicknesses.Further by way of example only, regions 36 and 40 can be fabricated tocomprise essentially the same stoichiometry or differentstoichiometries. Accordingly, FIG. 2 depicts but one example where thehigh k capacitor dielectric region includes a layer where a middleregion has a different stoichiometry than both inner and outer regions.

In an additional or alternate aspect or consideration, consider a high kcapacitor dielectric region comprising a layer of metal oxide havingmultiple different metals bonded with oxygen, where one of the metalswhen bonded with oxygen produces a first material having a first currentleakage potential. Further, absence of the one metal in the oxidecreates a vacancy and a second material having a second current leakagepotential which is greater than the first current leakage potential. Anexample would be a multiple metal component titanate, such as bariumstrontium titanate, where the one metal comprises titanium. Inaccordance with this implementation, the metal oxide layer comprises atleast one portion having a greater concentration of the first materialwhich is more proximate at least one of the first and second electrodesthan another portion which is more proximate a center of the layer.

Again, FIG. 2 illustrates an exemplary construction, whereby at leastone of portions 36 and 40 can be fabricated to have a greaterconcentration of the first material than another portion 38. Again usingbarium strontium titanate as an example, titanium constitutes a metal insuch material which, when bonded with oxygen, produces greater currentleakage potential or resistance than when a vacancy is created in theoxide by absence of the titanium atoms. Accordingly, barium andstrontium quantity could essentially be constant throughout the layer ofcapacitor dielectric region 35, with only the quantity of titaniumvarying relative to such regions such a described in the preferredexample immediately above.

In an additional or alternate considered aspect of the invention,consider a high k capacitor dielectric region comprising a layer ofmetal oxide having multiple different metals bonded with oxygen, whereone of the metals when bonded with oxygen has a first dielectricconstant. Another of the metals of such layer when bonded with oxygenhas a second dielectric constant which is less than the first dielectricconstant. The layer comprises at least one portion having a greaterconcentration of the one metal bonded with oxygen more proximate acenter of the layer than another portion more proximate either of thefirst and second electrodes. By way of example only, barium strontiumtitanate constitutes one such material. Specifically, barium andstrontium in such material constitutes metals which, when bonded withoxygen, produce a first dielectric constant which is greater than whentitanium is bonded with oxygen. Accordingly, and again by way of exampleonly and in reference to the above FIG. 2, region 38 constitutes the oneportion having a greater concentration of the one metal (i.e., one orboth of barium and strontium) bonded with oxygen which is more proximatea center of the layer.

In an additional or alternate considered aspect of the invention,consider a high k capacitor dielectric region comprising a layer ofmetal oxide having multiple different metals bonded with oxygen, whereone of the metals when bonded with oxygen produces a first materialhaving a first dielectric constant. Absence of the one metal in theoxide creates a vacancy, and a second material having a seconddielectric constant which is less than the first dielectric constant.The metal oxide layer comprises at least one portion having a greaterconcentration of the first material which is more proximate a center ofthe layer than another portion which is more proximate either of thefirst and second electrodes.

Again using barium strontium titanate as an example, barium andstrontium are example metals whose absence in the lattice when producingvacancies results in a dielectric constant which is less than whenpresent. Accordingly in this example with respect to barium strontiumtitanate, the one metal comprises at least one of barium and strontium.An exemplary construction encompassing the same is again as depicted inFIG. 2.

The above-described preferred embodiment was with respect to multiplecomponent titanates wherein both the current leakage potential anddielectric constant aspects of the invention are met in the samematerial. Alternate materials are also, of course, contemplated wherebyperhaps only one of the current leakage potential relationship or thecapacitor dielectric constant relationship results, with the inventiononly being limited by the accompanying claims appropriately interpretedin accordance with the Doctrine of Equivalents.

FIG. 3 depicts an exemplary process of depositing a dielectric layercomprising metal oxide having multiple different metals bonded withoxygen in accordance with an aspect of the invention. A chemical vapordeposition chamber 70 has a substrate 72 upon which deposition isdesired positioned therein. Exemplary multiple gas inlets 76, 77, 78 and80 are depicted schematically as extending to chamber 70. Fewer or moregas inlets could, of course, be provided. Further, gases could be mixedfurther upstream of the schematic depicted by FIG. 3, and flowed asmixtures or combinations relative to one or more inlets.

Multiple gaseous precursors are fed to the chamber under conditionseffective to deposit the dielectric layer having multiple differentmetals bonded with oxygen on substrate 72. At least some of theprecursors comprise different metals of the respective multipledifferent metals bonded with oxygen, which is deposited in the layer onthe substrate. As one example, a process for depositing (Ba,Sr) TiO₃includes utilizing precursors of Ba(DPM)₂, Sr(DPM)₂ and Ti(OC₃H₇)₄, O₂at 0.5 Torr and 410° C., where “DPM” denotes “dipivaloylmethanato”. Forexample, one of each of these gases could be flowed from the respectiveinlets 76, 77, 78 and 80. In accordance with one implementation, theflow of at least one of the precursors is varied during the feeding toachieve different concentrations of the different metals bonded withoxygen at different depths in the deposited layer.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1-31. (canceled)
 32. A semiconductor device comprising: a substratecomprising a conductive diffusion region; a first conductive layer inelectrical communication with the conductive diffusion region; a singleinsulative layer over the first conductive layer and comprising a high kdielectric material, the insulative layer having a thickness andcomprising three different metals and a varying stoichiometry of atleast one of the metals across the thickness, a first portion of theinsulative layer comprising a first concentration of one metal, and asecond portion of the insulative layer over the first portion andcomprising a second concentration of the one metal which is differentfrom the first concentration, the first portion comprising a dielectricconstant which is less than a dielectric constant of the second portion;and a second conductive layer over the insulative layer.
 33. The deviceof claim 32 wherein the one metal comprises barium.
 34. The device ofclaim 33 wherein the second concentration of barium is greater than thefirst concentration.
 35. The device of claim 32 wherein the one metalcomprises strontium.
 36. The device of claim 35 wherein the secondconcentration of strontium is greater than the first concentration. 37.The device of claim 32 wherein the one metal comprises titanium.
 38. Thedevice of claim 37 wherein the second concentration of titanium is lessthan the first concentration.
 39. The device of claim 32 wherein thesemiconductor device is a capacitor comprised by a memory cell.
 40. Thedevice of claim 32 wherein the semiconductor device is a capacitorcomprised by a memory array.
 41. A semiconductor device comprising: asubstrate comprising a conductive diffusion region; a first conductivelayer in electrical communication with the conductive diffusion region;a single insulative layer over the first conductive layer and comprisinga high k dielectric material, the insulative layer having a thicknessand comprising three different metals and a varying stoichiometry of atleast one of the metals across the thickness, a first portion of theinsulative layer comprising a first concentration of one metal, and asecond portion of the insulative layer over the first portion andcomprising a second concentration of the one metal which is differentfrom the first concentration, the first portion comprising a currentleakage potential which is greater than a current leakage potential ofthe second portion; and a second conductive layer over the insulativelayer.
 42. The device of claim 41 wherein the second concentration ofthe one metal is less than the first concentration.
 43. The device ofclaim 41 wherein the semiconductor device is a capacitor comprised by amemory cell.
 44. The device of claim 41 wherein the semiconductor deviceis a capacitor comprised by a memory array.
 45. The device of claim 41wherein the one metal comprises titanium.
 46. A method of forming acapacitor comprising: providing a first electrode over a substrate;forming a dielectric layer over the first electrode and comprising highk dielectric material, the forming of the dielectric layer comprising:forming a first portion proximate the first electrode; forming a centerportion over the first portion; and forming a third portion over thecenter portion, the center portion comprising a thickness which issubstantially the same as a thickness of at least one of the first andthird portions, and at least one of the portions comprising a dielectricconstant and/or a current leakage potential that is different from atleast one of the other two portions; and providing a second electrodeover the third portion of the dielectric layer.
 47. The method of claim46 wherein the first portion comprises a thickness which issubstantially the same as the thickness of the center portion.
 48. Themethod of claim 46 wherein the second portion comprises a thicknesswhich is substantially the same as the thickness of the center portion.49. The method of claim 46 wherein the first and second portionscomprise respective thicknesses which are substantially the same as thethickness of the center portion.
 50. The method of claim 46 wherein thecenter portion comprises a dielectric constant that is greater thanrespective dielectric constants of the first and third portions.
 51. Themethod of claim 46 wherein the center portion comprises a currentleakage potential that is less than respective current leakagepotentials of the first and third portions.
 52. The method of claim 46wherein the first portion comprises a current leakage potential that issubstantially the same as a current leakage potential of the thirdportion.
 53. The method of claim 46 wherein the capacitor is comprisedby a memory cell.
 54. The method of claim 46 wherein the capacitor iscomprised by a memory array.